At time t=0, a particle is located at the point (2,6,6). It travels in a straight line to the point (3,1,8), has speed 7 at (2,6,6) and constant acceleration i - 5j + 2k. Find an equation for the position vector r(t) of the particle at time t. The equation for the position vector r(t) of the particle at time t is r(t) = ([D i+ (D) j+ (D) k. (Type exact answers, using radicals as needed.)